1. Technical Field
This invention relates to a method of distributing data packets of system software in a point-to-multipoint system from a send unit to a plurality of receive units.
2. Discussion of Related Art
In a point-to-multipoint system, particularly a service-on-demand system, a server is provided as a send unit, and the receive units are decoders. The decoders are designed as set-top boxes. The system software of the set-top boxes needs to be updated when a new version of the system software is available.
From an article by Carl W. Symborski, xe2x80x9cUpdating Software And Configuration Data In A Distributed Communications Networkxe2x80x9d, Proceedings of the Computer Networking Symposium, IEEE Comput. Soc. Press, 1988, pages 331-338, a procedure for distributing data packets of system software in a point-to-multipoint system is known. The procedure is executed in a receive unit and consists of the following steps:
1. Wait until a predetermined period of time has expired or a notice has been received that a new version of the system software may be available.
2. Request information from the server as to whether a new version is available.
3. Compare the version communicated by the server with the version available in the receive unit.
4. If no change is detected, return to step 1.
5. If a change is detected, request the new version from the server.
6. Replace the old version with the new one.
7. Store the new version.
8. Return to step 1.
Thus, to obtain the new version of the system software, this procedure always requires an action by the receive unit together with a request to the server. If a plurality of receive units are present, each receive unit must request the new version by itself. Because of the structure of the distribution system, the new version, which is generally identical for all receive units, is transmitted from the send unit to the receive units separately. If there are 500 receive units, the send unit must transmit the new version 500 times, once to each receive unit. This takes a certain time. Thus, the transmission of further information is unnecessarily blocked, at least in a predetermined frequency range, for a certain period of time.
From an article by K. Rath and J. W. Wendorf, xe2x80x9cSet-Top Box Control Software: a Key Component in Digital Videoxe2x80x9d, Philips Journal of Research (1996), Vol. 50, No. 1/2, pages 185-199, a method of distributing data packets of system software in a point-to-multipoint system is known in which a receive unit designed as a set-top box obtains a new version of the system software telemetrically via a network. The set-top box sends a request to the server or obtains the new version from the server automatically on a periodic basis. The former corresponds essentially to the procedure described above. The latter involves the establishment of a connection between the server and an individual set-top box, which eliminates the need for the set-top box to actively request a new version but does not prevent the multiple transmission of the same information.
It is therefore an object of the invention to provide a method whereby the system software can be updated in a simple manner.
According to the invention, this object is attained by a method of distributing data packets of system software in a point-to-multipoint system from a send unit to a plurality of receive units, is characterized in that the following steps are taken one after the other:
1. An announce signal containing the information that the system software or part thereof will subsequently be transmitted is transmitted from the send unit to all receive units simultaneously.
2. The system software or part thereof is transmitted in the form of data packets from the send unit to all receive units simultaneously. The method is characterized in that by advance information in the form of an announce signal which is transmitted to all receive units by the broadcast method, the receive units are notified of the forthcoming transmission of the current version of the system software, whereupon they can prepare for the reception of the new version. The new version is also transmitted by the broadcast method, and ideally only once. If individual receive units should not have received the advance information, the method may, for example, be automatically repeated at a later time or the remaining receive units may request the new version from the server separately. Thus, compared with the prior art, the transmission time is ideally shortened by a factor corresponding to the number of receive units present, i.e., by a factor 500 if there are 500 receive units. If, for example, 10% of the receive units should not have received the advance information, the transmission time is still shortened by a factor of 250 (in case of automatic repetition) or approximately 100 (if separate requests are made).